A truck plowed into pedestrians Friday outside a busy department store in Stockholm, Sweden, killing four people and injuring 15 others in what the prime minister described as a "terror attack."

A national manhunt was under way for those responsible and one person was arrested in connection with the attack. Stockholm's central train station was evacuated and all trains in and out of the city were canceled. Nearby buildings were locked down for hours.

The attack was the latest in a string of similar assaults involving vehicles in Europe, including in Nice in the south of France, and in London and Berlin.

Swedish Prime Minister Stefan Lofven makes a statement after people were killed when a truck crashed into a department store in Stockholm, Sweden April 7, 2017.

Swedish Prime Minister Stefan Lofven said the incident was certainly a "terrorist attack." He added, "The government is doing everything in its power to find out what has happened."

Photos taken at the scene show the vehicle was a truck belonging to beermaker Spendrups, which said that its truck had been carjacked earlier in the day.

Witnesses say the truck drove straight into the entrance of the Ahlens department store on Drottninggatan, the city's biggest pedestrian street, sending shoppers screaming and running. Television footage showed smoke coming out of the store after the crash.

Sweden's King Carl Gustaf expressed his condolences for the victims and their families in a brief statement.

"We follow developments, but as of now our thoughts go to the victims and their families,'' he said. The king cut short a visit to Brazil on Friday to return home.

A number of European leaders, including German Chancellor Angela Merkel and London's mayor, Saddiq Khan, have released statements indicating their solidarity with Sweden.

"One of Europe's most vibrant and colorful cities appears to have been struck by those wishing it — and our very way of life — harm," said European Commission President Jean-Claude Juncker. "Attack on any of our [EU] member states is an attack on us all."

French President Francois Hollande voiced his "horror and indignation" over the assault and Paris Mayor Anne Hidalgo said the Eiffel Tower's lights will be turned off from midnight Friday in solidarity.

In neighboring Finland, President Sauli Niinisto called the attack a "maniac act of terror," while Danish Prime Minister Lars Loekke Rasmussen said it was a cowardly attempt "to subdue us and the peaceful way we live in Scandinavia."

The U.S. State Department also condemned the attack, adding, "Attacks like this are intended to sow the seeds of fear, but in fact they only strengthen our shared resolve to combat terrorism around the world."